Very rare item, in very good condition. These were only made circa 1982 for the Arri 3C, but are compatible with the 2C as well. 24 or 25 fps crystal switchable. Or, switch to variable mode (non-crystal) for other speeds. I was told the small 4-pin port is for connecting a speed controller for getting crystal sync at other speeds. Powers from 12V 4-pin XLR connector. Can run forwards or reverse - it has a switch for that. It needs a phenolic gear to connect to the drive gear at the bottom of the camera, but that's included with this motor. The motor has captive screws to attach to your 2C or 3C. No power cable included.